JP2000146510A - Thickness detector and picture image recorder using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable high-precision detection by a simple construction by providing a movable magnetic substance arranged on the surface of an object touching it, and a magnetic field sensor which detects the magnitude of a magnetic field generated by the magnetic substance as the thickness of the object. SOLUTION: A thickness detector provided between the sheet feeding cassete and recording head of a laser printer, etc., is provided with, for example, a movable core 10 which touches a sheet A and changes its position, and a Hall element sensor 20 which is fixed to the periphery of the movable core and detects a magnetic field generated by the movable core. The movable core 10 is a magnet in the shape of an approximately rectangular parallelopipede obtained by magnetizing neodymium, etc., for example, and is fitted to the frame C of the printer, etc., through the use of a spring 11. Since the magnitude of a magnetic field to be detected is inversely proportional to the square of the quantity of the position displacement of the movable core which corresponds to the thickness of the sheet A, the thickness of the sheet A is detected by the output signal of the Hall element sensor 20. A magnetic field sensor can also be constituted by using an oscillation circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a PPC (Plain Pape).
The present invention relates to a thickness detecting device for detecting the thickness of a sheet or the like as an object, and an image recording device using the same, which is used for an image recording device such as an RBP (Laser Beam Printer).

[0002]

2. Description of the Related Art In a printer of the electrophotographic process system, if the toner fixing temperature is controlled at a fixed value irrespective of the thickness of a sheet, the fixing property of the toner is deteriorated and the quality of image quality is deteriorated. Some have a function of detecting the thickness of the toner and changing the toner fixing temperature in accordance with the detection result. This type of printer is provided with a thickness detecting device for detecting the thickness of the sheet.

A conventional thickness detector irradiates a sheet with laser light generated by a semiconductor laser light emitting element, and receives the laser light reflected at this time by a semiconductor laser light receiving element.
This is a basic configuration in which the thickness of a sheet is detected based on a change in the wavelength of the laser light (referred to as a first conventional example). There is also a configuration in which the thickness of a sheet is detected using a potentiometer (referred to as a second conventional example).

In a printer not provided with such a thickness detecting device, when data on the type of paper and its thickness is input, the toner fixing temperature is changed according to the input data.

In an ink-jet printer, if recording is not performed in a state where the distance between the nozzle head and the paper is always constant, the pixels become wider or narrower, and the shape of the pixels is deformed. Therefore, an adjustment lever for adjusting the distance between the nozzle head and the sheet is provided. When the type of paper is changed, the thickness of the paper changes and the distance between the nozzle head and the paper changes slightly. Therefore, in this case, it is necessary to check the thickness of the paper and finely adjust the adjustment lever.

[0006]

However, in the case of the first conventional example, the configuration of the peripheral circuits of the semiconductor laser light emitting element and the semiconductor laser light receiving element is complicated, and it is difficult to reduce the cost. . On the other hand, in the case of the second conventional example, since it is necessary to use mechanical parts such as a potentiometer, there is a disadvantage that the detection accuracy is low.

In a printer not provided with such a thickness detecting device, the cost can be reduced by omitting the device, but data of the type of paper and its thickness can be input. It becomes necessary or it is necessary to finely adjust the distance between the nozzle head and the paper using an adjustment lever, and it is pointed out that the usability is poor in this respect.

SUMMARY OF THE INVENTION The present invention has been made in view of the above background, and has as its object the thickness detecting device and the device capable of achieving high precision because of its very simple configuration. To provide an image recording apparatus using the same.

[0009]

A thickness detecting device according to the present invention is a thickness detecting device for detecting the thickness of an object,
A movable magnetic body disposed at a position in contact with the surface of the object and movably provided to be displaced by the contact; and a movable magnetic body fixed around the movable magnetic body. And a magnetic field sensor for detecting the magnitude of the magnetic field generated by the sensor as the thickness of the object.

In such a configuration, the position of the movable magnetic body is displaced in accordance with the thickness of the object, and accordingly, the magnitude of the magnetic field generated by the movable magnetic body detected by the magnetic field sensor also changes. Therefore, the signal output from the magnetic field sensor is a signal corresponding to the thickness of the object.

According to another aspect of the present invention, there is provided a thickness detecting device, comprising: a movable magnetic body; a detecting member disposed at a position in contact with a surface of the object; A support / guide mechanism that movably supports or guides a detection member that is displaced by contact with the upper part, and detects a magnetic field fixed around the movable magnetic body and created by the movable magnetic body as a thickness of the object. And a magnetic field sensor.

According to such a configuration, the detecting member on which the movable magnetic body is attached moves according to the thickness of the object, and accordingly, the magnitude of the magnetic field generated by the movable magnetic body detected by the magnetic field sensor also increases. Change. Therefore, the signal output from the magnetic field sensor is a signal corresponding to the thickness of the object.

More preferably, a Hall element sensor is used as the magnetic field sensor. In such a case,
Just supply a predetermined operating voltage to the Hall element sensor,
A voltage corresponding to the thickness of the object is output from the Hall element sensor.

More preferably, a magnetic field sensor having the following configuration may be used. First and second coils that are magnetically coupled to each other and that are arranged so that the inductance changes according to the displacement of the movable magnetic body;
A first oscillation circuit that oscillates at a constant oscillation frequency and outputs a signal to a first coil; and a capacitor that forms a resonance circuit between the second coil and the first coil. The second coil and the capacitor constitute a tuning circuit that tunes to the oscillation frequency of the oscillation circuit when the movable magnetic body is at a predetermined position.

In such a configuration, the tuning circuit including the first and second coils and the capacitor is tuned at the oscillation frequency of the oscillation circuit with the movable magnetic body at a predetermined position. Therefore, the impedance of the tuning circuit is minimized. On the other hand, when the movable magnetic body is displaced from the predetermined position, the inductances of the first and second coils change accordingly, and the resonance frequency of the tuning circuit also changes. That is, since the resonance frequency of the tuning circuit deviates from the oscillation frequency of the oscillation circuit,
The impedance of the tuning circuit increases. As described above, since the impedance of the tuning circuit changes according to the position of the movable magnetic body, the output of the tuning circuit changes according to the position of the movable magnetic body. Since the position of the movable magnetic body is displaced in accordance with the thickness of the object, the output of the tuning circuit is in accordance with the thickness of the object.

More preferably, a magnetic field sensor having the following configuration may be used. That is, the third and fourth coils wound around a core that forms a magnetic circuit with the movable magnetic body.
And oscillates at a constant oscillation frequency
And a second oscillating circuit for outputting to the second coil.

In such a configuration, when the third coil is excited by a signal output from the second oscillation circuit, a voltage is generated in the fourth coil by electromagnetic induction.
However, since a magnetic circuit is formed between the core around which the third and fourth coils are wound and the movable magnetic body, if the position of the movable magnetic body is displaced according to the thickness of the object, the magnetic circuit is The resistance changes, and the voltage generated in the fourth coil changes accordingly.

Further, the image recording apparatus using the thickness detecting device of the present invention has a function of changing the fixing temperature, the recording head driving time, or the interval between the recording head and the paper according to the type or thickness of the paper. An image recording apparatus, wherein a thickness of a sheet as an object is detected by the above-described thickness detecting device, and a fixing temperature, a recording head driving time, or an interval between the recording head and the sheet is changed according to the detection result. It is characterized by being.

In such a configuration, when the thickness of the sheet changes, the fixing temperature, the recording head driving time, or the interval between the recording head and the sheet is automatically adjusted accordingly.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. Here, a thickness detecting device provided in an electrophotographic process type laser printer as an image recording device will be described.

FIG. 1 is a schematic view of the apparatus, FIG. 2 is a block diagram of a control circuit of the laser printer, FIG. 3 is a schematic view for explaining a first modification of the thickness detection apparatus, and FIG. It is a figure for demonstrating a 2nd modification, (a) is a schematic side view, (b) is a schematic front view which showed only one part, and FIG. 5 is a 3rd modification of a thickness detection apparatus. It is a figure for explaining an example, (a) is a schematic side view, (b) is an exploded perspective view, FIG. 6 is a side view for explaining a modification of a magnetic field sensor, and FIG. FIG. 8 is a circuit diagram, and FIG. 8 is a schematic diagram for explaining another modification of the magnetic field sensor.

The laser printer takes out paper A from a paper supply cassette (not shown) disposed on the left side of the drawing by a feed roller 40, and attaches a base plate to a recording head section (not shown) disposed on the right side of the drawing. The recording head unit has a basic configuration in which an image is recorded on the sheet A by the recording head unit. This laser printer is provided with a thickness detecting device for controlling the toner fixing temperature and the like according to the thickness of the paper A.

This thickness detecting device is a device for detecting the thickness of a sheet A as an object on the surface of a base plate B. A movable core provided between the sheet supply cassette and the recording head unit, the movable core being disposed at a position where it comes into contact with the surface of the sheet A, and movably provided so as to be displaced by the contact; 10 (corresponding to a movable magnetic body)
And a Hall element sensor 20 (corresponding to a magnetic field sensor) fixed to the periphery of the movable core 10 and detecting the magnitude of the magnetic field generated by the movable core 10 as the thickness of the paper A. I have.

The movable core 10 uses a substantially rectangular parallelepiped magnet magnetized with neodymium, samarium cobalt, ferrite, or the like.
Is mounted via a spring 11. The movable core 10 applies a load F to the base plate B by the spring 11.
It has been pressed. When there is no paper A, the lower surface of the movable core 10 is in direct contact with the base plate B.
The size of the weight F is such that the paper A is composed of the movable core 10 and the base plate B.
And the movable core 10 according to the thickness of the paper A.
Is set to such a value that the position can be displaced in the upward direction without difficulty. In order to allow the paper A to smoothly enter between the movable core 10 and the base plate B, curved surfaces 101 as shown are formed at both ends of the lower surface of the movable core 10.

The Hall element sensor 20 is arranged at a position facing the movable core 10 and is fixed to the back side of the base plate B. The output signal of the Hall element sensor 20 is input to a control circuit of the laser printer. This control circuit is as shown in FIG.

In the figure, reference numeral 50 denotes a CPU (Central Processing Unit) for processing a control program for controlling the entire laser printer, and reference numeral 51 denotes a constant voltage for driving the Hall element sensor 20. It is a constant voltage circuit. CP
The Hall element sensor 20 is connected to the I / O port of U50 via a buffer 52, an amplifier 53, and an A / D converter 54, so that the output signal of the Hall element sensor 20 is input in a digital form. Has become. Also, CPU
A fixing temperature adjusting circuit 55 is connected to another I / O port 50, and a signal for operating the fixing temperature adjusting circuit 55 is output from the port.

The CPU 50 calculates the amount of displacement of the movable core 10 based on the output signal of the Hall element sensor 20 and outputs this to the fixing temperature adjusting circuit 55 as a signal.

The fixing temperature adjusting circuit 55 is a heater energization control circuit for adjusting the toner fixing temperature, and is configured to perform negative feedback control of the toner fixing temperature using a signal output from the CPU 50 as a target value.

The operation of the thickness detecting device constructed as described above and the laser printer related thereto will be described.

First, the detection principle of the thickness detection device will be described. When there is no sheet A, the lower surface of the movable core 10 is in contact with the base plate B, and the movable core 10 is at the lowest position. That is, the movable core 10 is located closest to the Hall element sensor 20, and the magnitude of the magnetic field generated by the movable core 10 detected by the Hall element sensor 20 indicates the largest value. On the other hand, when the paper A is present, the paper A
The movable core 10 is displaced upward according to the thickness of the movable element 10, the movable core 10 is slightly separated from the Hall element sensor 20, and the magnitude of the magnetic field generated by the movable core 10 detected by the Hall element sensor 20 is smaller than the above. Become smaller.

The magnitude (H) of the magnetic field detected by the Hall element sensor 20 is determined by the amount of displacement (d
R) is inversely proportional to the square. The displacement (dR) of the movable core 10 is equal to the thickness of the sheet A here. This is because the movable core 10 is displaced in the vertical direction according to the thickness of the sheet A. Therefore, the thickness of the sheet A can be detected with high accuracy only by the output signal of the Hall element sensor 20.

The reason why the thickness of the sheet A can be detected with high accuracy is that not only the magnetic field detection resolution of the Hall element sensor 20 is extremely high, but also the lower surface of the movable core 10
The movable core 10 is brought into contact with the sheet A by this contact.
There is also a point that the position is displaced in accordance with the thickness of the device and no mechanism is interposed in the process of displacing the position. It has been confirmed that such a thickness detecting device can detect the thickness of the sheet A on the order of about 0.05 mm.

In the CPU 50, the movable core 1 is determined based on the magnitude (H) of the magnetic field indicated by the output signal of the Hall element sensor 20.
The position displacement amount (dR) of 0, that is, the thickness of the paper A is calculated, a value corresponding to the thickness of the paper A is set as a target value of the toner fixing temperature, and the set value is sent to the fixing temperature adjustment circuit 55 as a signal. Output.

Therefore, even if the thickness of the paper A changes due to the type of the paper A or the thickness of the paper A varies, the fixing temperature adjustment circuit 55 functions to control the current paper A. The temperature is automatically adjusted to an appropriate toner fixing temperature according to the thickness. As a result, the fixability of the toner is reduced and the quality of the image quality is not reduced.

In the case of the thickness detecting device as described above, it is possible to detect the thickness of the sheet A with high accuracy by using only the movable core 10, the spring 11, and the Hall element sensor 20, as shown in FIG. Not only is the mechanism very simple, but also because the Hall element sensor 20 is of a voltage output type, necessary peripheral circuits include a constant voltage circuit 51, a buffer 52, an amplifier 53, and A /
Since only inexpensive circuit components such as the D converter 54 are required, the overall configuration is very simple. Moreover, since the detection accuracy of the thickness of the paper A does not greatly affect the mounting accuracy of the Hall element sensor 20, it is possible to significantly reduce the cost as a whole.

Note that the weight F may be applied to the sheet A only by the weight of the movable core 10. In this case, although the spring 11 becomes unnecessary, the movable core 10
A guide is required to make the robot movable. Except for the constant voltage circuit 51, the buffer 52 and the like are necessary as an interface circuit between the Hall element sensor 20 and the CPU 50, and may be omitted in some cases. Further, instead of the fixing temperature adjustment circuit 55, an adjustment adjustment circuit such as a toner density may be used.

Since such a thickness detecting device is provided in the laser printer, the cost can be greatly reduced, and a troublesome operation such as inputting the data of the thickness of the paper A becomes unnecessary. , Convenience is also improved.

Here, the laser printer of the electrophotographic process system has been described, but the present invention is similarly applicable to an ink jet printer. In this case, CP
The fixing temperature adjusting circuit 55 according to the signal output from U50
, But the recording head drive time adjusting circuit 56 or the head interval adjusting mechanism 57 is operated by the same signal.

The recording head driving time adjustment circuit 56 is a circuit for adjusting the amount of ink discharged from the nozzle head per pixel as the driving time of the recording head, and performs recording per pixel in accordance with a signal output from the CPU 50. This is a basic configuration for changing the driving time of the head. in this case,
The drive time of the recording head per pixel is automatically adjusted according to the thickness of the sheet A.

On the other hand, the head interval adjusting mechanism 57 is a mechanism for adjusting the interval between the nozzle head and the sheet by a stepping motor or the like, not by an adjusting lever.
Has a basic configuration in which the amount of rotation of a stepping motor or the like is changed in accordance with a signal output from the controller. In this case, the interval between the nozzle head and the paper A is automatically and constantly maintained irrespective of the thickness of the paper A.

The ink jet printer has the same advantages as the electrophotographic laser printer. Also, unlike before,
It is not necessary to finely adjust the distance between the nozzle head and the paper using the adjustment lever, and the usability is also improved in this respect.

Next, a first modification of the thickness detecting device will be described with reference to FIG. This thickness detecting device is disposed at a position where it comes into contact with a magnet 12 (corresponding to a movable magnetic material) magnetized with neodymium, samarium cobalt, ferrite, etc., and on the surface of the sheet A sent out by the feed roller 41. Paper A and a detection lever 30 (corresponding to a detection member)
A rotary shaft 31 (corresponding to a support mechanism) that movably supports a detection lever 30 that is displaced by contact with the surface of the sensor.
And a Hall element sensor 20 fixed around the magnet 12 and detecting the magnetic field generated by the magnet 12 as the thickness of the paper A.

The detection lever 30 is a substantially non-magnetic flat plate made of a non-magnetic material, and is movable about a rotation shaft 31 in the direction of the arrow shown in FIG. It comes into contact with the top. The base end of the detection lever 30 is attached to a frame C of the laser printer via a spring 32. The tip of the detection lever 30 is pressed against the surface of the sheet A with a load F by the spring 32. The Hall element sensor 20 is fixed at a position below the base end of the detection lever 30. For other configurations, including the setting of the magnitude of the load F,
This is exactly the same as the case of the thickness detecting device shown in FIG.

In the case of such a thickness detecting device, the detecting lever 30 rotates in the direction of the arrow in accordance with the thickness of the sheet A, and the position of the magnet 12 is displaced. The distance changes. Therefore, it is possible to detect the thickness of the sheet A with high accuracy just like the case of the thickness detecting device shown in FIG. However, comparing the dimension from the rotation axis 31 to the tip of the detection lever 30 and the dimension from the rotation axis 31 to the magnet 12, the latter is larger than the former,
The amount of displacement of the magnet 12 with respect to the change in the thickness of the magnet is large, and it is not necessary to use a Hall element with high detection resolution, which is advantageous in this point.

The detecting member is not limited to a bent member such as the detecting lever 30, but may be a linear member, for example. In this case, the magnet 12 is attached to the base end of the detection member, and it is necessary to provide a guide mechanism for movably guiding the detection member instead of the rotating shaft 31 as a support mechanism. .

That is, as the detection member moves up and down in accordance with the thickness of the sheet A, the position of the magnet 12 is displaced, and the Hall element sensor 20 detects this amount of displacement as the thickness of the sheet A. Will be. In short, Figure 1
The operation is exactly the same as that of the thickness detecting device shown in FIG.

Next, a second modification of the thickness detecting device will be described with reference to FIG. This is the detection member
And a guide plate 43 that supports both shafts 401 of the feed roller 40 (only one is shown in the figure) as a support mechanism. A spring 44 is mounted between the guide plate 43 and the base plate B. The spring 44 is for ensuring that the paper A on the base plate B is sent out by friction with the surface of the feed roller 40.

Although such a feed roller 40 and the like are existing in a conventional laser printer, a shaft 401
A magnet 12 magnetized with neodymium, samarium cobalt, ferrite, or the like is attached to the tip of the device, and a Hall element sensor 12 is attached near the magnet. That is, the feed roller 40 moves in the vertical direction according to the thickness of the paper A, and the position of the magnet 12 is also displaced accordingly. (The support mechanism means that the guide plate 43 supports the magnet 12 movably. Works). The displacement of the magnet 12 is detected by the Hall element sensor 12 as the thickness of the sheet A. However, if the feed roller 40 is soft, the thickness of the paper A is absorbed, so that a hard roller is preferably used.

The use of such a thickness detecting device is advantageous in that the existing mechanism as a laser printer can be fully utilized, no major design change is required, and the cost can be reduced.

Next, a third modification of the thickness detecting device will be described with reference to FIG. A magnet roller 41 as a movable magnetic body is provided below the feed roller 40, and the Hall element sensor 20 as a magnetic field sensor is fixed below the magnet roller 41.

The magnet roller 41 is formed by forming a magnet magnetized with neodymium, samarium cobalt, ferrite or the like into a roller shape, and the guide plate B is axially supported by a leaf spring 33 attached to the back side. The magnet roller 41 passes through the opening 1 formed in the plate B.
It comes in contact with. The magnet roller 41 is attached to the back side of the guide plate B via a leaf spring 33.

The leaf spring 33 is a rectangular thin plate made of resin, and has an opening 331 in the center portion thereof into which the main body of the magnet roller 41 enters. Recesses 332 that support the axis 411 of the magnet roller 41 are formed respectively.

As shown in FIG. 5A, when the paper A enters between the feed roller 40 and the magnet roller 41, the magnet roller 41 is displaced downward by the thickness of the paper A, and accordingly, is displaced. The distance between the magnet roller 41 and the Hall element sensor 20 changes. Therefore, the thickness of the sheet A can be detected by the Hall element sensor 20 in exactly the same manner as the thickness detection device shown in FIG.

In the case of such a thickness detecting device, FIG.
As compared with the above-described apparatus, it is not necessary to newly add the movable core 10, and the material of the feed roller 40 and the pair of rollers are basically replaced with a magnetic material except for the Hall element sensor 20. Since it is only necessary to use the printer, it is not necessary to make a large change in the design of the printer, and it is possible to further reduce the cost in this regard. Further, since the installation space of the thickness detecting device does not matter, there is an advantage in reducing the size of the printer.

Next, a modification of the magnetic field sensor will be described using the thickness detecting device shown in FIG. 1 as an example. Here, a magnetic field sensor 60 as shown in FIGS. 6 and 7 is used instead of the Hall element sensor 20. However, the movable core 10 is made of nickel zinc ferrite.

The magnetic field sensors 60 are coils L1, L2 (corresponding to the first and second coils) which are magnetically coupled to each other and arranged so that the inductance changes according to the displacement of the movable core 10. The oscillation circuit 110 oscillates at a constant oscillation frequency and outputs the signal to the coil L1.
(Corresponding to a first oscillation circuit), and a capacitor C2 and the like forming a resonance circuit between the coil L2 and the like.
The oscillation of the oscillation circuit 110 is performed by the coils L1 and L2 and the capacitor C2 in a state where the movable core 10 is at the reference position (here, there is no sheet A and the lower surface of the movable core 10 is in contact with the base plate B). A tuning circuit 120 that tunes to the frequency is configured. Oscillation circuit 100 and tuning circuit 1
An amplification circuit 110 is provided between the control circuit 20 and the detection circuit 130. A detection circuit 130 is provided at an output stage of the tuning circuit 120. The magnitude of the magnetic field generated by the movable core 10 is output from the detection circuit 130 as a voltage.

The detailed circuit configuration of the magnetic field sensor 60 will be described with reference to FIG. Vcc indicates the power supply voltage supplied to the magnetic field sensor 60.

The oscillation circuit 100 includes a ceramic oscillator CO,
It comprises resistors R2, R3, capacitors C3, C4, and a transistor Q1, oscillates at a constant oscillation frequency α, and outputs a signal to the tuning circuit 120 via the amplifier circuit 110. The oscillation circuit 110 is roughly composed of a negative resistance circuit (resistances R2 and R3, capacitors C3 and C4 and a transistor Q1) and a resonator (ceramic oscillator CO).

The oscillation frequency α is selected from several MHz to several tens MHz for economical reasons. That is, when the frequency is reduced, the inductance of the coils L1 and L2 of the tuning circuit 120 and the capacitance of the capacitors C1 and C2 are increased and it is necessary to use a dimensionally large one. This is because handling becomes difficult and cost increases. Also, the reason why the ceramic resonator CO is used as the resonator is as follows.
This is because it is cheaper than a crystal oscillator or the like, and the oscillation frequency can be easily stabilized.

The amplifier circuit 110 is provided between the oscillation circuit 100 and the resonance circuit 121 (described later), and amplifies the output signal of the oscillation circuit 100. It is composed of a coupling capacitor C5, resistors R4 and R5, and a transistor Q2.

Since the output signal of the oscillation circuit 110 is amplified by the amplification circuit 110, not only does the resonance circuit 121 operate stably, but also because the impedance between the base and collector of the transistor Q2 is high, the oscillation circuit The isolation between the resonance circuit 100 and the oscillation circuit 100 is sufficiently ensured, and the oscillation circuit 100 oscillates stably irrespective of the resonance circuit 121.

The tuning circuit 120 includes a resonance circuit 121 in which a coil L1 and a capacitor C1 are connected in parallel, and a coil L1
Circuit 122 in which capacitor 2 and capacitor C2 are connected in parallel
It is composed of

The inductances of the coils L1 and L2 and the capacitances of the capacitors C1 and C2 are selected so as to tune to the oscillation frequency α when the movable core 10 is at the above-described reference position. The reference position may be set in any manner, and may be selected or tuned to the oscillation frequency α in a state where the movable core 10 is at the infinite position.

In order to improve the stability with respect to the change of the ambient temperature, here, the coil L2 and the capacitor C2 having the opposite temperature characteristics are used.
Temperature compensation is performed. Resonant circuits 121, 12
The reason for using the parallel resonance circuit as 2 is to simplify the circuit configuration. That is, since the voltage output method is used, additional circuits such as a current / voltage conversion circuit become unnecessary when a parallel resonance circuit is used.

The detection circuit 130 includes a coupling capacitor C6, diodes D1 and D2, a resistor R6, a capacitor C7, and a buffer amplifier OP1, detects a signal output from the tuning circuit 130, and buffers the detected signal. The signal is output to the OUTPUT terminal via the amplifier OP1.

The time constant of the resistor R6 and the capacitor C7 is
It is desirable to increase the input level of the buffer amplifier OP1 so as not to fluctuate due to the ripple. However, as the time constant increases, not only does the outer shape of the capacitor C7 increase, but also the cost increases. Therefore, here, the constant value of the resistor R6 is set to about several hundred kΩ to several MΩ, and the capacitance of the capacitor C7 is set to 0. It is selected to be about 0.01 F to several F.

Next, will be described with reference to FIG. 6 the internal structure of the magnetic field sensor 60. In the figure, 61 is a substantially cylindrical resin case, 62 is a substrate on which the above-mentioned circuit components except for the coils L1 and L2 are mounted, and 64 is a nickel-zinc ferrite around which the coils L1 and L2 are wound. The core.

A coil L is provided inside the tip of the case 61.
1, a core 64 around which L2 is wound is attached.
The end surface of the core 64 is exposed from the case 71 and faces the lower surface of the base plate B.

The coil L1 and the coil L2 are arranged coaxially with the core 64. The coil L1 is located on the lower side in the figure, in other words, at a position away from the movable core 10, and the coil L2 is located on the upper side in the figure, in other words. , Are arranged at a position close to the movable core 10.

The coils L1 and L2 and the capacitors C1 and C2 mounted on the board 62 are connected via lead wires (not shown). In order to reduce the length of the lead wire and make it less susceptible to noise, the coils L1, L2
In addition, other circuit components are incorporated in the magnetic field sensor 60.

Although not shown, a connector is provided on the outer surface of case 61, and power supply voltage Vcc is input through this connector, while detection circuit 130
Is output.

The operation of the magnetic field sensor 60 configured as described above will be described. First, when the power supply voltage Vcc is supplied, the sensor operates, and the oscillation circuit 100 oscillates at a constant oscillation frequency α irrespective of the displacement position of the movable core 10. Circuit 121
Is input to

When there is no paper A and the movable core 10 is at the reference position, the tuning frequency of the tuning circuit 120 is equal to the oscillation frequency α, the impedance as the tuning circuit 30 is minimum, and the output from the tuning circuit 120 is obtained. The signal level becomes maximum, and the voltage output from the detection circuit 130 also becomes maximum.

On the other hand, when the sheet A is fed and the movable core 10 is displaced in accordance with the thickness of the sheet A, the coils L1, L
2, the tuning frequency of the tuning circuit 30 deviates from the oscillation frequency α, and the impedance of the tuning circuit 30 also increases.
Therefore, the level output from the tuning circuit 30 is lower than that described above. The voltage output from the detection circuit 130 also decreases. More specifically, the change in the resonance frequency of the resonance circuit 122 including the coil L2 depends on the coil L1
Is larger than the change in the resonance frequency of the resonance circuit 121 including the above, and the change in the resonance frequency is detected by the detection circuit 130 as a change in the tuning.

As described above, the voltage output from the detection circuit 130 has a value corresponding to the thickness of the sheet A, and highly accurate detection is performed in the same manner as when the Hall element sensor is used.
This is because the magnitude of the magnetic field generated by the movable core 10 and, consequently, the thickness of the paper A are detected when the Q value of the tuning circuit 30 is high.

Further, while the coil L1 is disposed at a position away from the sheet A and the coil L2 is disposed at a position near the sheet A, the input impedance of the coil L1 is low and the output impedance of the coil L2 is high. The circuit configuration is used, and this is one of the factors that make the detection accuracy extremely high. This is because the coil L1 is less likely to be affected by the surrounding noise magnetic field, while the coil L2 detects a change in the magnetic field only in the vicinity thereof with high sensitivity. Note that it is more effective if the shields are arranged around the coils L1 and L2.

The input impedance of the coil L1 is low because one end of the coil L1 is connected to the power supply and the other end is grounded via the collector and the emitter of the transistor Q2 and the resistor R5. The output impedance of the coil L2 is high because one end of the coil L2 is grounded, and the other end is connected to a buffer amplifier OP1 via a coupling capacitor C6 and a diode D3.
Because it is connected to the input.

Further, a capacitor C1 is connected in parallel with the coil L1.
To form the resonance circuit 121, the voltage at both ends of the coil L1 becomes maximum when the movable core 10 is at the reference position, and this point is also a factor that makes the detection accuracy extremely high. is there.

From the above, it is possible to stably detect the amount of displacement of the movable core 10, that is, the thickness of the sheet A with high accuracy. Also, including the fact that only one oscillation circuit 100 is required, the circuit configuration is very simple compared to the same type of magnetic field sensor that detects a magnetic material by changing the inductance of the coil, and it is necessary to use expensive circuit components. Since there is no such device, it is possible to reduce the cost.

The coils L1 and L2 are magnetically coupled to each other, and as long as the coils L1 and L2 are arranged so that the inductance changes according to the displacement of the movable core 10, the arrangement and positional relationship between the coils L1 and L2 are changed. The connection may be made by one coil using an intermediate tap.

The oscillation circuit 100 may have any configuration as long as it can generate and output a signal of a fixed frequency, and may use an inverter IC, an OP amplifier, or the like.

The capacitor C2 which forms the resonance circuit 122 with the coil L2 may be a series resonance circuit or another composite resonance circuit.

The same applies to the tuning circuit 120. The movable core 10 is controlled by the coils L1, L2 and the capacitor C2.
Is the reference position, the oscillation frequency α of the oscillation circuit 100 is
Any configuration may be used as long as the circuit configuration tunes to the above configuration, and the capacitor C1 that forms the resonance circuit 121 with the coil L1 may be omitted.

The detection circuit 130 includes the magnetic field sensor 6
If it is not necessary to set the voltage output format to 0, this can be omitted. In this case, the tuning circuit 12
Since the frequency and the like of the high-frequency signal output from 0 changes according to the thickness of the paper A, the magnetic field sensor 60 has a high-frequency signal output format.

Next, another modified example of the magnetic field sensor will be described using the thickness detecting device shown in FIG. 1 as an example. Here, instead of the Hall element sensor 20, a magnetic field sensor 70 as shown in FIG. 8 is used. However, the movable core 10 is made of a material such as neodymium, samarium cobalt, or ferrite-nickel zinc-based ferrite.

The magnetic field sensor 70 listed here has a U-shaped iron core 71 having a magnetic circuit formed with the movable core 10.
Coils L3 and L4 (corresponding to third and fourth coils) wound around the oscillating circuit 140 and an oscillating circuit 140 (corresponding to a second oscillating circuit) which oscillates at a constant oscillation frequency and outputs a signal to the coil L3. ) And the like. In addition, an amplification circuit 150 and a detection circuit 160 are sequentially connected to an output stage of the coil L4.

The operation of the magnetic field sensor 70 thus configured will be described. When the coil L3 is excited by a signal output from the oscillation circuit 140, an AC voltage is generated in the coil L4 by electromagnetic induction. However, coil L3,
Since the magnetic circuit L4 forms a magnetic circuit between the core 71 and the movable core 10, when the movable core 10 is displaced in accordance with the thickness of the sheet A, the magnetic resistance changes, and the magnetic resistance is generated in the coil L4. The level of the AC voltage changes, and the output voltage of the detection circuit 160 also changes. More specifically, when the paper A enters between the movable core 10 and the base plate B, the magnetic resistance between the movable core 10 and the core 71 increases, and the magnetic flux in the core 71 decreases. The level of the voltage induced at L4 decreases. Therefore, similarly to the magnetic field sensor 60 shown in FIG. 6, the thickness of the sheet A can be detected with high accuracy.

However, the detection circuit 160 and the amplification circuit 1
If the magnetic field sensor 70 does not need to be of the voltage output type, it can be omitted. In this case, since the level of the AC voltage generated in the coil L <b> 4 changes according to the thickness of the paper A, the magnetic field sensor 70 is of an AC output type.

The shape and material of the core 71 may be any as long as the movable core 10 and the magnetic circuit are formed. The design may be changed so that a permanent magnet is used instead of the coil L3 and a Hall element sensor is used instead of the coil L4. In this case, the oscillation circuit 140 and the detection circuit 1
It is possible to omit 60.

The thickness detecting device according to the present invention is not limited to detecting the thickness of the paper of the image recording apparatus, but can detect the thickness of any object as long as it is a non-magnetic material. It is. In addition, the shape and material of the movable magnetic body are not limited to the above embodiment.

Further, the image recording apparatus using the thickness detecting device according to the present invention is not limited to application only to a laser printer.
Naturally, it is also applicable to PPC and the like.

[0092]

As described above, according to the thickness detecting device of the first aspect of the present invention, the position of the movable magnetic body is displaced in accordance with the thickness of the object, and the positional displacement is detected by the magnetic field sensor. Therefore, the thickness of the object can be detected with high accuracy. Moreover, the overall configuration is very simple, and cost reduction can be achieved.

In the thickness detecting device according to the second aspect of the present invention, the position of the movable magnetic body is displaced together with the detecting member in accordance with the thickness of the object, and the positional displacement is detected by the magnetic field sensor. Therefore, there is the same advantage as in claim 1.

In the case of the thickness detecting apparatus according to the third aspect of the present invention, a Hall element sensor is used as the magnetic field sensor. Since a voltage corresponding to the thickness of the magnetic field sensor is output, the peripheral circuit of the magnetic field sensor becomes very simple, and further reduction in cost can be achieved in this respect.

In the case of the thickness detecting device according to the fourth aspect of the present invention, since the position displacement of the movable magnetic body according to the thickness of the object is detected as a change in the resonance frequency of the tuning circuit, the thickness of the object is detected. The thickness of the object can be detected with high accuracy.

In the thickness detecting apparatus according to the fifth aspect of the present invention, a combination of an oscillation circuit and a transformer is used as a magnetic field sensor, and a voltage corresponding to the thickness of the object is output. Therefore, except for the point that an oscillation circuit is required, there is no difference from the case where the Hall element sensor is used, and there is the same merit as in claim 4.

In the case of the image recording apparatus using the thickness detecting device according to the sixth aspect of the present invention, when the thickness of the sheet changes, the fixing temperature, the recording head driving time, or the interval between the recording head and the sheet changes accordingly. It is automatically adjusted, so there is no need to input data on the type of paper and its thickness or finely adjust the distance between the nozzle head and the paper using the adjustment lever. become. Moreover, since the thickness of the object is detected with high accuracy by the thickness detecting device and the configuration is very simple, it has great significance in reducing the cost and improving the performance of the entire device.

[Brief description of the drawings]

FIG. 1 is a view for explaining an embodiment of the present invention, and is a schematic view of a thickness detecting device.

FIG. 2 is a block diagram of a control circuit of a laser printer provided with the apparatus.

FIG. 3 is a schematic diagram for explaining a first modification of the device.

FIGS. 4A and 4B are diagrams for explaining a second modification of the apparatus, in which FIG. 4A is a schematic side view, and FIG. 4B is a schematic front view showing only a part.

FIGS. 5A and 5B are views for explaining a third modification of the apparatus, in which FIG. 5A is a schematic side view, and FIG. 5B is an exploded perspective view.

FIG. 6 is a side view for explaining a modification of the magnetic field sensor which is a component of the device.

FIG. 7 is a circuit diagram of the magnetic field sensor.

FIG. 8 is a schematic diagram for explaining another modification of the magnetic field sensor.

[Explanation of symbols]

 A paper B base plate 10 movable core 20 Hall element sensor

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Shinichi Saeki 1-4-3 Kitakyuho-ji Temple, Yao-shi, Osaka Ho-Siden Co., Ltd. F-term (reference) 2F063 AA16 BA30 BB01 BC09 CA09 GA05 GA29 GA42 GA53 LA05 LA07 LA11 LA19 2G017 AA04 AB05 AC04 AC08 AD04 AD05 AD21 AD53 BA03 BA05 BA13 BA15 BA18

Claims (6)

[Claims] 1. A thickness detecting device for detecting the thickness of an object, wherein the thickness detecting device is disposed at a position in contact with a surface of the object and movably provided to be displaced by the contact. A movable magnetic body, and a magnetic field sensor fixed around the movable magnetic body and detecting a magnitude of a magnetic field generated by the movable magnetic body as a thickness of the object. 2. A thickness detecting device for detecting the thickness of an object, comprising: a movable magnetic body; and a detecting member disposed at a position in contact with a surface of the object and having the movable magnetic body attached thereto. A support / guide mechanism that movably supports or guides a detection member that is displaced by contact with the surface of the object; and a magnetic field that is fixed around the movable magnetic body and is generated by the movable magnetic body. A thickness detecting device comprising: a magnetic field sensor that detects a thickness of an object. 3. The thickness detecting device according to claim 1, wherein a Hall element sensor is used as the magnetic field sensor. 4. A magnetic field sensor comprising: a first coil and a second coil which are magnetically coupled to each other and whose inductance is changed according to a displacement of a movable magnetic body; And a capacitor that forms a resonance circuit between the first and second coils, and a capacitor that forms a resonance circuit between the first and second coils. 3. The thickness detecting device according to claim 1, wherein the coil and the capacitor constitute a tuning circuit that tunes to the oscillation frequency of the oscillation circuit when the movable magnetic body is at a predetermined position. 5. A magnetic field sensor comprising: a third and a fourth coil wound around a core having a magnetic circuit formed between the movable magnetic body and a movable magnetic body; The thickness detecting device according to claim 1, further comprising a second oscillation circuit that outputs a signal to a coil. 6. An image recording apparatus having a function of changing a fixing temperature, a recording head driving time, or an interval between a recording head and a sheet according to a type or a thickness of the sheet. A thickness detecting device for detecting a thickness of a sheet as an object by using the apparatus, and changing a fixing temperature, a recording head driving time, or an interval between the recording head and the sheet in accordance with the detection result. Image recording device using the same.